Milestone And Time-And-Materials Billing: A Guide For Services Firms

You have won the work. Now you have to decide how to charge for it, and that decision will shape your cash flow, your margin, and roughly half of your client conversations for the next six months.

Milestone and time-and-materials billing are the two structures most project-driven services firms end up choosing between. One ties payment to delivered outcomes. The other tracks payment to effort spent. They allocate risk in opposite directions; they hit your bank account on different rhythms, and they place very different demands on your delivery and finance teams.

This guide covers what each model is, how they compare, when each one fits, how to combine them, and what changes on the tax and revenue-recognition side depending on which you pick. It is written for firms in the 25 to 150 person range running client projects in consulting, IT services, engineering, legal, or agency work.

Milestone And Time-And-Materials Billing At A Glance

Milestone billing invoices the client when a defined stage of work is completed and accepted. The trigger is an event, and the amount is agreed in advance.

Time-and-materials billing invoices the client for hours worked at agreed rates, plus the cost of materials and expenses. The trigger is elapsed effort, and the amount is known only after the fact.

The practical difference comes down to one question: are you selling a defined outcome, or are you selling capacity? If the scope is firm enough that you can commit to what “done” looks like, milestone billing works. If the scope will move as the work reveals itself, time and materials is the safer structure for both sides.

Most firms run both, on different accounts, and often inside the same contract.

What Is Milestone Billing?

Milestone billing is a payment structure where the client pays a pre-agreed amount each time the firm completes, and the client accepts, a defined deliverable or project stage. A discovery phase, a design sign-off, a system go-live, and a post-launch handover might each carry their own percentage of the total contract value.

Four things have to exist for it to work:

• A defined deliverable. Something the client can point at and say it exists.
• Acceptance criteria. A written test for whether the milestone is met, agreed before work starts.
• An assigned value. A fixed amount or a percentage of the contract value attached to each milestone.
• An approval step. A named person on the client side who signs off, with a time limit on how long they can take.

Milestone billing is common in engineering and construction-adjacent work, software implementation, architectural design, and any engagement where the client’s own finance team wants to release budget against visible progress rather than against elapsed time.

It is worth separating milestone billing from two things it gets confused with. Progress billing invoices against percentage completion, which is a measurement of effort rather than an accepted deliverable. Fixed-fee billing sets one price for the whole engagement and may be invoiced on a calendar schedule with no link to delivery at all. Milestone billing sits between them, because the price is fixed while the invoice still has to be earned.

What Is Time-And-Materials Billing?

Time-and-materials billing charges the client for the hours your team logs at contractually agreed rates, plus materials, expenses, and any pass-through costs. There is no fixed total. The invoice reflects what happened.

The clearest definition of the model comes from US federal procurement rules, which have had to describe it precisely for decades. Under the Federal Acquisition Regulation, a time-and-materials contract provides for acquiring supplies or services on the basis of direct labor hours at specified fixed hourly rates that include wages, overhead, general and administrative expenses, and profit, plus actual cost for materials. That single sentence contains the whole mechanism, since your rates carry the margin while materials pass through at cost.

The same rules are candid about the model’s weakness. FAR 16.601 states that a time-and-materials contract may be used only when it is not possible at the time of placing the contract to estimate the extent or duration of the work accurately or to anticipate costs with any reasonable degree of confidence. It goes further, noting that the model provides no positive profit incentive to the contractor for cost control or labor efficiency, which is why buyer-side surveillance of performance is required. And it builds in a guardrail: a T&M contract must include a ceiling price that the contractor exceeds at its own risk.

You do not have to be selling to a government to take those three points seriously. They describe exactly why clients get nervous about open-ended hourly billing, and exactly what you need to put in the contract to settle that nervousness. Read the full text at FAR 16.601 on the eCFR if you are drafting a rate card.

Milestone Billing Vs Time And Materials Billing: The Core Differences

Dimension	Milestone Billing	Time-And-Materials Billing
Invoice trigger	Completion and acceptance of a defined deliverable	Hours logged and expenses incurred in a period
Total contract value	Fixed at signing	Estimated, with an optional ceiling
Who carries scope risk	The firm	The client
Who carries cost risk	The firm	The client
Budget certainty for the client	High	Low without a cap
Margin predictability for the firm	Low if estimates are wrong	High per hour, variable in total
Change handling	Formal change order, renegotiated value	Absorbed into the next invoice
Invoice frequency	Irregular, tied to delivery	Regular, usually monthly
Administrative load	Acceptance tracking and sign-off chasing	Timesheet discipline and backup detail
Best suited to	Firm scope, defined outcomes, staged approvals	Evolving scope, discovery work, ongoing support
Common failure mode	Milestone disputes stall payment	Client questions hours, disputes the invoice

Who Carries The Risk In Each Model

Under milestone billing, you have committed to a price for a defined outcome. If the work takes 40 percent longer than you estimated, that overrun comes out of your margin. The client’s exposure is capped at the contract value. Firms price this risk in, usually with a contingency buffer, which is the honest reason milestone and fixed-price work often looks more expensive per hour than the equivalent T&M engagement.

Under time and materials, the position reverses. Every additional hour is billable, so an underestimate becomes the client’s cost rather than yours. Your exposure sits in the rate card: if your rates do not cover fully loaded cost plus target margin, you lose money on every hour regardless of how many you bill.

Scope movement is where both models get tested, and it is more common than most contracts assume. PMI’s 2018 Pulse of the Profession found that 52% of projects completed in the prior twelve months experienced scope creep or uncontrolled changes to scope, up from 43% five years earlier. On a milestone contract, movement shows up as unbilled work you absorb, while on a T&M contract it shows up as an invoice the client did not expect. Neither is comfortable, and both are best handled by a change-order process written into the contract before anyone needs it.

What Each Model Does To Your Cash Flow

Milestone billing produces lumpy cash. You might invoice nothing for seven weeks, then raise 30 percent of a contract value in one go. That is fine when your milestones are frequent, and your acceptance cycle is fast. It becomes a problem when a single sign-off slips, because one delayed approval can push a large invoice across a quarter boundary while your payroll runs on schedule regardless.

Time and materials produces smoother cash. Monthly invoicing against logged hours gives you a predictable rhythm and a shorter gap between doing the work and asking for the money. The tradeoff is that revenue tracks utilization, so a slow month on delivery is a slow month on collections.

Two practical levers matter more than the model choice itself:

• Advance or mobilization payments. A percentage of the contract value invoiced at kickoff funds the early phase of a milestone engagement, which is where your costs are highest and your billing events are furthest away.
• Acceptance windows. Write a fixed number of days for client review into the contract, with deemed acceptance after that window expires. Without it, your cash flow is governed by your client’s calendar.

If cash timing is the constraint you are trying to solve rather than a side effect, our guide to project cash flow covers the forecasting side in more detail.

When Milestone Billing Is The Right Call

Milestone billing fits when most of the following are true:

• The scope is defined well enough that you can write acceptance criteria for each stage today.
• The client’s budget process releases funds against deliverables rather than against time.
• The engagement has natural, visible breakpoints. A design freeze, a pilot, a go-live.
• You have delivered similar work before, and your estimates are grounded in your own historical data rather than optimism.
• The client is comfortable with a formal change-order process, and so are you.
• The relationship benefits from shared checkpoints, which is often the case with a new client who has not worked with you before.

It fits poorly on advisory retainers, on discovery and research work, on maintenance and support, and on anything where the deliverable is a judgment rather than an artifact. If you cannot describe what “accepted” means in a sentence, the milestone will be disputed.

When Time-And-Materials Billing Is The Right Call

Time and materials fits when:

• The scope will be discovered during the work rather than before it.
• The client wants to redirect priorities mid-engagement without renegotiating a contract each time.
• The engagement is open-ended: staff augmentation, managed support, ongoing advisory.
• Speed to start matters more than price certainty, because you can begin without a completed scoping exercise.
• You have the timesheet discipline to produce credible, line-level backup on demand.

That last point carries more weight than it looks. T&M billing is a trust model. The client is paying for effort they cannot directly observe, so the quality of your time records is the product as far as the invoice conversation is concerned. Firms that reconstruct timesheets from memory at month-end tend to have longer collection cycles, because their invoices invite questions. If timesheet hygiene is the gap, our timesheet management guide walks through the operating habits that close it.

The Hybrid Structures Most Firms Run

In practice, very few engagements are purely one model. Three hybrids cover most of what services firms use.

Capped Time And Materials

You bill hourly, but the contract carries a not-to-exceed ceiling. The client gets budget certainty. You get paid for effort. If you approach the cap, work pauses pending a written extension. This is the structure the federal rules described above effectively mandate, and it resolves the single biggest client objection to hourly billing.

The discipline it requires is real-time visibility of consumed budget against the cap. A ceiling you discover you have breached is a ceiling that costs you money.

Phased Fixed Fee

Each phase is separately scoped and separately priced, and the next phase is only committed once the prior one closes. The discovery phase is often run as T&M, and the build phase as milestone billing once the discovery output makes accurate estimation possible. This is the most common shape in implementation and engineering work, and it is a sensible default when a client wants price certainty on work that is not yet certain.

Milestone Base Plus Time-And-Materials Change Orders

The core scope is billed against milestones. Anything outside it is billed hourly through an approved change order. This protects your margin from scope creep without forcing a renegotiation of the whole contract every time the client asks for something extra.

The requirement here is a clear scope boundary written in the original contract. Without one, every request becomes an argument about which side of the line it falls on.

How To Build A Milestone Schedule That Gets Paid

A milestone schedule is a payment instrument, so write it like one.

1. Break the project at real delivery events. Tie milestones to things that exist when they are done, not to calendar dates. A date-based milestone is a fixed-fee installment wearing a costume.
2. Write acceptance criteria for each one. Specific, testable, and agreed in the contract. “Client approval” is not a criterion. “Signed UAT report covering the twelve test cases in Annexure B” is.
3. Weight the early milestones. Costs are front-loaded on most projects, and payment should partly follow. A common shape is a mobilization payment, then progressively smaller installments, with a final tranche on handover.
4. Cap the acceptance window. Fourteen days is typical. State that the milestone is deemed accepted if no written objection arrives in that period.
5. Decide the retention position up front. If the client will hold back a percentage until final handover, price for it and forecast for it.
6. Name the approver. One person, with a named alternate. Sign-off that routes to a committee routes to nobody.
7. Attach a change-order clause. Define what triggers one, who approves it, and how the work is repriced.

The failure mode worth designing against is rarely the missed milestone. It is the one delivered on time, uncontested, and still unsigned three weeks later because the approver is traveling.

How To Run Time-And-Materials Billing Without Losing Client Trust

Time and materials collapses when the client stops believing the hours. Five habits keep it healthy.

• Publish the rate card by role, and hold it. Rates by seniority, stated in the contract, with a defined annual escalation. Ad hoc rates invite renegotiation on every invoice.
• Bill rates at the time the work was done. If a consultant’s rate changes in June, March’s work should still bill at March’s rate. Systems that apply today’s rate retroactively create disputes you will lose.
• Log time daily, at task level. Weekly reconstruction produces round numbers, and round numbers look invented.
• Send backup detail with every invoice. Date, person, task, hours. Clients who can audit an invoice rarely feel the need to.
• Flag budget consumption before the client asks. A monthly note saying 62 percent of the ceiling is consumed against 58 percent of the scope is the cheapest trust-building exercise available to you.

Tax And Revenue Recognition Under Each Billing Model

This is the part most comparisons skip, and it is where the two models diverge most sharply for your finance team.

When The Invoice Has To Be Raised In India

Milestone engagements usually qualify as a continuous supply of services under GST, which has its own invoice-timing rules. Under Section 31(5) of the CGST Act, where the due date of payment is ascertainable from the contract, the invoice must be issued on or before that due date; where it is not ascertainable, the invoice must be issued before or at the time the supplier receives payment; and where payment is linked to the completion of an event, the invoice must be issued on or before the date that event is completed.

That third clause is the one that governs milestone billing directly, and it catches firms out. The obligation to raise the tax invoice attaches to the completion of the milestone event, not to the date the client gets around to signing the acceptance note. If your acceptance cycle regularly runs weeks past completion, your invoice timing and your GST position can drift apart. The primary text sits on the CBIC tax information portal.

When The Supply Is Dated In The UAE

For firms billing into the GCC, the UAE VAT Decree-Law handles staged and periodic billing under its own provision. Article 26 sets the date of supply for any contract that includes periodic payments or consecutive invoices as the earliest of the date a tax invoice is issued, the date payment is due as shown on the tax invoice, or the date payment is received, provided it does not exceed one year from the date the goods or services were provided. The one-year backstop matters on long engineering and construction programs, where a phase can run past twelve months without a billing event.

Confirm the current position against the VAT Decree-Law published by the Federal Tax Authority, and check the executive regulations alongside it, since the invoice-issuance timeline is set separately.

Billing Is Not Revenue Recognition

Under IFRS 15 and its US equivalent, revenue is recognized as performance obligations are satisfied, which frequently does not line up with when you invoice. On a milestone contract, you may have delivered two months of work with no billing event yet reached, which leaves a contract asset on the balance sheet rather than a receivable. Your billed number and your recognized revenue number will differ, and both are correct.

Time and materials has an easier path. IFRS 15 paragraph B16 offers a practical expedient: if an entity has a right to consideration from a customer in an amount that corresponds directly with the value to the customer of the performance completed to date, such as a service contract where the entity bills a fixed amount for each hour of service provided, the entity may recognize revenue in the amount to which it has a right to invoice. For a straight hourly engagement, billed and recognized can be the same number, which removes a whole reconciliation exercise at period close.

None of this should decide your billing model. It should decide how early your finance team gets told which model you signed. Speak to your own tax adviser on how these provisions apply to your contracts.

A Decision Checklist For Choosing Your Billing Model

Work down the list. The first firm “no” usually points you toward time and materials.

• Can you write testable acceptance criteria for every stage of this work today?
• Do you have historical delivery data from at least two comparable engagements?
• Is the client’s requirement stable, or still forming?
• Does the client’s budget process release funds against deliverables or against periods?
• Can you absorb a 30 percent overrun on this engagement without it hurting?
• Do you have a named client-side approver with authority to sign off?
• Is your timesheet data good enough today to defend an hourly invoice line by line?
• Can you see consumed budget against contract value in real time, or only at month-end?
• Does the contract need a ceiling to get signed?
• Will this engagement generate change requests, and is there a process for them?

If you answered yes to the first six, milestone billing is a reasonable bet. If the seventh and eighth are weak, fix those before you commit to either model, because both depend on them.

The Operational Layer Both Models Depend On

There is a pattern we see repeatedly in firms between 25 and 150 people. The billing model gets chosen in the contract, and then the systems turn out to be unable to support it.

Milestone billing needs someone to know, at any moment, how much of a contract value has been billed, how much remains, and which milestones are delivered but unsigned. When that lives in a spreadsheet maintained by one person, milestones get missed, invoices get raised late, and occasionally an invoice gets raised for more than the order has left in it.

Time and materials need approved, project-tagged, rate-attached hours that flow into an invoice without anyone retyping them. When timesheets sit in one tool, and invoicing sits in another, month-end becomes a reconciliation exercise, and the hours that were never logged are simply gone.

Juntrax is built for that seam. It is the project-to-cash operations layer for services firms, sitting alongside the accounting system you already use rather than replacing it. Time logged against a project carries the rate that applied on the day the work was done, which is what keeps a mid-year raise from rewriting an old invoice. An invoice can be built directly from a project’s billable time, so approved hours become invoice lines without a manual step. And every invoice is booked against the client’s purchase order, with the system blocking any invoice that exceeds the order’s remaining balance, which is the single most useful guardrail milestone billing can have.

On the Cash-Flow side, the order’s own screen shows order total, billed, received, remaining, pending, and overdue in one view, so the question “how much of this contract is left to bill” has an answer rather than an investigation. Prices freeze when you bill, so a catalogue change next quarter does not rewrite an invoice you already sent.

Firms running staged engineering programs, phased implementations, and matter-based legal work all hit the same wall from different directions. If you want the longer view of how that chain runs end to end, we documented how we run our own billing inside Juntrax, and the PSA buyer guide for small consulting firms covers what to look for if you are evaluating platforms.

Choosing Between Milestone And Time-And-Materials Billing

Milestone and time-and-materials billing are tools for different conditions, and the honest answer to “which is better” is that it depends on how much you know about the work before you start. Defined scope, defined outcomes, and a client who buys against deliverables point to milestones. Moving scope, discovery work, and open-ended support point to time and materials. Most firms end up running a hybrid, and the ones who do it well have written the change-order process before they needed it.

What does not change is the operational requirement underneath. Whichever model you choose, you need hours you can defend, contract values you can see against, and invoices that come out of your delivery data rather than out of someone’s memory.

Frequently Asked Questions

What Is The Difference Between Milestone Billing And Time And Materials Billing?

Milestone billing invoices a pre-agreed amount when a defined deliverable is completed and accepted, so the total contract value is fixed, and the firm carries the risk of overrun. Time-and-materials billing invoices for hours worked at agreed rates plus materials, so the total is variable, and the client carries the cost risk. Milestone billing suits defined scope; time and materials suits evolving scope.

Can You Use Milestone And Time-And-Materials Billing In The Same Contract?

Yes, and most mature services contracts do. The common structure bills the core defined scope against milestones and handles anything outside that scope through approved change orders billed hourly. Another frequent shape runs the discovery phase on time and materials, then switches to milestone billing for the build phase once the scope is firm enough to estimate accurately.

Which Billing Model Is Better For Cash Flow?

Time and materials generally produces smoother, more predictable cash because you invoice monthly against logged hours. Milestone billing produces lumpier cash tied to delivery events, which can be stronger overall if milestones are frequent and acceptance is fast, and weaker if a single sign-off delays a large invoice. A mobilization payment at kickoff and a capped acceptance window are the two levers that most improve milestone cash flow.

What Is A Not-To-Exceed Clause In Time-And-Materials Billing?

A not-to-exceed clause sets a ceiling on total billable value. You bill hourly up to that ceiling, and work pauses beyond it pending a written extension. It gives the client budget certainty while preserving the flexibility of hourly billing, and it is standard practice in federal contracting, where a T&M contract must carry a ceiling price the contractor exceeds at its own risk.

When Should A Milestone Invoice Be Raised Under GST?

For a continuous supply of services where payment is linked to the completion of an event, Section 31(5) of the CGST Act requires the tax invoice to be issued on or before the date that event is completed. Where the due date of payment is ascertainable from the contract, the invoice is due on or before that date. Confirm your specific position with your tax adviser, since classification of the supply drives the answer.

Does Milestone Billing Determine When Revenue Is Recognized?

No. Under IFRS 15, revenue is recognized as performance obligations are satisfied, which often does not align with the milestone billing schedule. Work delivered ahead of a billing event typically sits as a contract asset. Time-and-materials engagements can often use the right-to-invoice practical expedient in IFRS 15 B16, which allows revenue to be recognized at the amount the entity has a right to invoice when that corresponds directly to the value delivered.

How Many Milestones Should A Project Have?

Enough that no single delayed sign-off puts a quarter of the contract value at risk, and few enough that each one represents a deliverable the client cares about. On a six-month engagement, four to six milestones is a common working range. Frequency should be driven by real delivery breakpoints rather than by a target number.